title: The vascular reactivity of melatonin.
abstract: 1. Melatonin receptors have been located in the vasculature. The present study investigates the hypothesis that melatonin can alter vascular contraction. 2. Helical strips of endothelium-intact rat thoracic aorta and endothelium-denuded mesenteric and endothelium-denuded caudal arteries were mounted in isolated tissue baths for measurement of isometric contractile force. Melatonin (10(-12)-10(-3) M) did not cause contraction in the thoracic aorta, the mesenteric artery or the caudal artery. In the same arteries contracted with phenylephrine, melatonin (10(-12)-10(-3) M) did not cause direct relaxation. 3. In the rat aorta, a test for inhibition of KCl-induced contraction was conducted. Melatonin (10(-5)-10(-3) M) and the melatonergic agonist N-acetylserotonin (10(-5) M) inhibited contraction to KCl. The percentage inhibition observed at 70 mM KCl were as follows for melatonin: [25.3% (1 x 10(-5) M), 32.0% (1 x 10(-4) M), 26.4% (3 x 10(-4) M), 52.4% (1 x 10(-3) M); N-acetylserotonin 26.7% (1 x 10(-5) M), no inhibition at (1 x 10(-3) M)]. The melatonergic antagonist luzindole (2 x 10(-6) M) did not inhibit the melatonin (10(-3) M)-induced inhibition of KCl contraction in the rat aorta. 4. The possible effect that melatonin may have on endothelial nitric oxide activity also was examined. Melatonin (10(-5) M) did not affect acetylcholine (10(-9)-10(-4) M)-induced relaxation in the rat aorta contracted with a half-maximal concentration of phenylephrine. 5. These data suggest that melatonin can inhibit rat vascular reactivity but does so largely in a non-specific manner.
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48824-1317, USA.
authors.forename: K K
authors.initials: KK
authors.lastname: Monroe
authors.forename: S W
authors.initials: SW
authors.lastname: Watts
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D004347:Drug Interactions; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013268:Stimulation, Chemical
chemical_list: D011189:Potassium Chloride; D008550:Melatonin; D000109:Acetylcholine